The distribution of adsorption energy of U(VI) onto AEPTES-functionalized porous silica with multiple average pore sizes

Amino-functionalized porous silica proved a powerful [U(VI)] adsorbent, yet the adsorption mechanism remains unclear. This study first produces porous silica with different surface areas and average pore sizes. A grafting agent, 3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane (AEPTES), is then used to modify the surface of the obtained porous silica. The mesoporous silica adsorbents are thoroughly characterized with SEM, BET, XPS, NMR, and zeta potentials. The adsorbents are used to adsorb [U(VI)], and experimental results are fitted by the Langmuir adsorption isotherm, Potential of Mean Force (PMF) model, and Surface Complex Formation Model (SCFM), as to estimate the adsorption energy delta G(ads)(0), which consists of specific chemical energy, delta G(chem)(0), coulombic energy, delta G(coul)(0), solvation energy, delta G(solv)(0), and lateral interaction energy, delta G(lat)(0). From the result of SCFM, the values of delta G(chem)(0) and delta G(coul)(0) are close, and both are the main contributor to delta G(ads)(0). The result also indicates that AE@MPS has the lowest surface activate site density in terms of U(VI) adsorption at pore size of 4.1 nm. This work provides a fundamental understanding of how amino groups bond to U(VI) cation in solution. It is a potential reference for the molecular design of uranium collectors.

Automated summary

Amino-functionalized porous silica was studied as an adsorbent for U(VI) and its adsorption mechanism was investigated. Different porous silica materials with varied surface areas and average pore sizes were synthesized and modified with AEPTES. The adsorbents were thoroughly characterized and the adsorption energy was estimated. It was found that both coulombic energy and chemical energy contributed significantly to the adsorption energy, and AE@MPS had the lowest surface activate site density at a pore size of 4.1 nm.